Postage value computing systems have been described in the art. Such systems, in response to weight information of the article to be mailed and its destination, determine the amount of postage to be applied. The required postage is a function of many variables such as, for example, different classes, whether for United States Postal Service (USPS) or United Parcel Service (UPS) or international service, etc. In addition, special fees may be selected and additional required postage for that must be computed.
In the U.S. Pat. No. 4,286,325 to D. F. Dlugos et al a postal value computing system is described which is capable of handling a wide range of postage variables. The system as schematically shown in FIG. 1 herein organizes the postage values in rate charts 22 occupying respective areas in a memory 24. Since rates are subject to change, the rate charts 22 are stored in physically replaceable memories 24 such as may be formed with programmable read-only memory (PROM) devices.
Computation of a postal value is commenced with the actuation of a key 26.1 in a keyboard 28 as described with reference to FIG. 5 in the U.S. Pat. No. 4,286,325 patent. A program operable in a processor (not shown in FIG. 1) connected to the keyboard 28 causes a transfer to a particular memory location 30.1 in a portion of a memory 32 referred to as a directory. The directory memory 32 contains in location 30.1 data which serves as a vector 32.1 (V.sub.1) to direct the program of the microprocessor to a start location 36.1 in rate memory 24 necessary to reach the rate charts 22 needed in response to the actuated key 26.1 and the article weight. As part of the process to reach a rate chart 22, the program recognizes that certain keys 26 need an additional code entry. This recognition is done in response to the analysis of the contents of rate memory location 36.1 to which the program was vectored by vector 32.1. The contents of rate memory location 36 is a definition byte 38 that causes the program to request from the operator, by way of a display prompt, the entry of a code. Such code defines a particular rate chart. For example, if the keyboard key 26.3 for express had been actuated, then the program requires entry of a numerical code with a numeric keyboard 39 to determine what kind of express mail is requested. The express mail may be domestic-same-day airport service requiring a two digit code 01, or international express-on-demand to Canada, code 13. Use of such codes are well known.
Once a code has been entered, the program derives from the successive locations 40 and 42 following the definition byte 38, a vector 44 that directs the program to the first part 46 of an index table 48 commencing at rate memory location 50.
Thus, in response to an analysis by the program of the signal generated by actuated key 26.1 and the subsequent code entries made by the operator the index table 48 is reached. The program then compares the entered code with those in the index 48 until a match is found, such as at 52, where the program finds an address of the pertinent rate chart such as 22.1.
Before the program derives a rate from a rate chart, an initial comparison, as described in the Dlugos patent, involves the start and stop weights applicable to that rate chart with the measured weight of the article for which postage is to be computed. This comparison determines whether the article weight is in the range of the rate chart and thus whether the chart should be used at all. In the event the article weight is outside the range of the rate chart, the program automatically advances to the next higher rate chart whose address location is stored with other data in the first or lower range rate chart.
The rate charts 22 frequently change as postal rates fluctuate. Hence, the many postage value computation systems 30 in the field require that their memories be frequently updated with new replaceable PROM memories for new rate charts. In addition, new directory memories are needed when rate charts are relocated in memory 24, for example, in response to a need to expand or add special rate chart increments and the like. Such updating of memories becomes expensive for the user, particularly when his use of an automatic postage value computing system 20 involves only particular rate charts so that he has no interest in having normally unused rate charts kept current.